The present invention relates to antithrombotic agents and more specifically to agents which inhibit blood platelet aggregation.
It is considered that cerebral apoplexy and myocardial infarction are mainly caused by thrombosis. In this regard, a thrombus formed by various reasons precedes arteriosclerosis as thrombus on the vessel wall; and when thrombus in the blood flow turns to emboli, the thus formed embolism causes blood circulation disorders. Arteriosclerosis and blood circulation disorders are considered to cause cerebral apoplexy and myocardial infarction.
Recent developments in the research of the function of blood platelets have established that the blood platelets mainly contribute to formation of the thrombus. That is, the blood platelets in the blood flow are in equilibrium state with the normal vessel walls, and causes no aggregate. However, when the blood vessels are injured, the blood platelets adhere to the collagen or the basement membrane in subintimal tissue of the blood vessels. This adhesion causes a release reaction of ADP and Serotonin from the dense body of the blood platelets. The ADP and Serotonin released from the platelets causes an aggregate reaction of the blood platelets thereselves, thus causing formation of a platelet aggregate. At the same time, released ADP and Serotonin also cause a release reaction of blood platelet factor 3; and the thus released blood platelet factor 3 accelerates Thrombin formation. As a result, the blood coagulation mechanism is accelerated by the thus formed Thrombin and a thrombus is formed.
Considering the important function of the blood platelets in the formation of thrombus as above described, drugs which inhibit the functions such as adhesion, release aggregation, etc. have been tried in the prevention of cure of thrombosis. Typical drugs which inhibit platelet aggregation are non-steroidal anti-inflammatory agents such as aspirin, indometacin, etc.; pyrasol derivatives such as sulphinpyrazone; pyrimidopyrimidine derivatives such as dipyridamole; adenosine derivatives, paraverine, etc. However, superior drugs in pharmaceutical effect and safety, are in demand.